Which of the following would be a voluntary risk factor for lung cancer?
a. smoking cigarettes
b. air pollution (smog)
c. asthma inhalers
d. family history of lung cancer

The answer is A. Smoking cigarettes
 
While most of these would cause a risk lung cancer, they are not voluntary. You can't control air pollution or a family history of lung cancer. However, you can control smoking cigarettes and you chose to smoke them so that would be a voluntary risk of getting lung cancer.
 
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Its simple its a because they are more fat